The invention relates generally to image processing and computer graphics. More specifically, the invention relates to compression of motion video utilizing wavelet transforms.
One important aspect of imaging is the transmission and encoding of image sequences (frames) for video which tries to its show time and space motion of a scene. Motion video compression techniques seek to reduce the bit rate required for storing or transmitting video while maintaining a certain level of acceptable video quality (as it is perceived). Most video sequences contain some amount of spatial redundancy within the same frame (intra-frame) or temporal redundancy between frames (inter-frame). By removing these redundancies, compression of data is achieved while distinguishing image features are retained. Intra-frame spatial redundacies are removed using transform coding similar to that used for compressing still images such as Discrete Cosine Transform (DCT). For removing temporal redundancy, techniques such as motion estimation and compensation are employed. FIG. 1 shows one such conventional video compression scheme widely used in existing video compression standards such as MPEG (Motion Picture Experts Group).
The encoder of FIG. 1 takes a current frame IN and subtracts it from a previous predicted frame I""Nxe2x88x921 which is fed back. The difference frame D is transform coded (block 110) to remove intra-frame redundancy and then subjected to quantization (block 120), which is the process of mapping a values spanning one range to another range with fewer members. For instance, linear quantization might simply divide any value in the original data set by 2, rounded to the closest value, thus reducing the range of values from K to K/2. The quantized and transform coded data is then subjected to an entropy encoder (block 130). During quantization, there may have been errors introduced into the image (which also provide for compression). To reduce the propagation of this error, a decoder (composed of inverse quantization) (block 125) and inverse transform coding (block 135) is used to recover a close approximation of the current frame. This approximation ANxe2x88x921 is added to the predicted frame generated by the previous cycle INxe2x88x921, which is held in a frame buffer (block 140). The error recovered data I""Nxe2x88x921 is sent to the inter-frame predictor (block 150) which employs motion estimation and compensation to output a predicted frame IN.
Such compression techniques are suitable for broadcasting applications, where the encoder can be dedicated and expensive hardware which relies on many low cost decoders on the receive end to extract the video. While good video quality is attainable from such an approach, it is not the most suitable for other applications. Where both encoding and decoding need to be low cost and more real-time, such as in personal computer video-conferencing, video phones and video cameras, the architecture of FIG. 1 is cost prohibitive and may not yield fast throughput demanded of a real-time system.
A method including intra-frame coding a first sequence of video data using Discrete Wavelet Transforms; and inter-frame coding a second sequence of video data using Discrete Wavelet Transforms, the second sequence of data interspersed with the first sequence.